1. Field of the Invention
This invention relates to impact printers. More specifically, it relates to a ribbon cartridge for impact printers.
2. Description of Prior Art
With the development of the printer field in the direction of high speed impact printers producing high quality printing suitable for correspondence at high speed in the order of 60 cycles per second, new needs have arisen with respect to printer ribbon structures and drive mechanisms.
Because of the high throughput of such printer apparatus and the consequently high volume of printed characters, the art has had to provide a ribbon which is of relatively low cost but yet provides high quality printing. Because of the difficulty in meeting these requirements with the more traditional fabric base or carbon film ribbons, the art has been working with a more recent type of ribbon which is a cast matrix of a plastic such as nylon containing liquid ink. While such ribbon structures appear to provide the combination of high quality printing and low cost, they are highly distortable and fragile. Further, they are sensitive to high temperature and high humidity. For example, at temperatures in the order of 25.degree. C. and 80% relative humidity, as little as 30 grams of ribbon tension may cause objectionable yielding and frequent breakage of a cast matrix type of ribbon which is in the order of 0.6 cm. wide.
In addition, because of the highly fragile nature of the ribbon, the ribbon cannot tolerate extensive strikeovers which cover or overlap the same ribbon area. Consequently, the ribbons may be used for one pass only which turns out to be a relatively expensive proposition when the cost of manufacturing the ribbon and packaging the ribbon in the ribbon cartridge is considered. Another approach involves the use of ribbon indexing means which step the ribbon through a plurality of vertical positions for each horizontal depth that the ribbon is moved. This requires a relatively expensive ribbon indexing mechanism in the printer.
The apparatus of the present invention achieves maximum utilization of ribbon area with minimal overstrikes or overlaps without ribbon indexing apparatus in the printer.